There currently exist numerous systems for detecting the presence of a user. Systems based on optical sensors, on temperature sensors, or on electrodes and capacitive sensors may be mentioned. The systems based on capacitive sensors are based on an evaluation of the variation in the capacitance of a variable capacitive structure as a function of the presence or otherwise of one or more users.
At present, there exist charge transfer capacitive sensors such as the sensors described in the publication “CAPACITIVE SENSORS” by Larry K. Baxter, published by The Institute Of Electrical and Electronic Engineers, Inc. The sensors presented in this publication allow the variation in the capacitance of a variable capacitor C1 to be measured, thanks to a capacitor C2 known as reference capacitor. By carrying out a cycle composed of a large number of charges and discharges of the capacitor C1 into the reference capacitor C2, until a fixed voltage threshold is reached across the terminals of the reference capacitor C2, the variation in the capacitance C1 with respect to the preceding cycle can be detected by estimating the variation in the number of discharges of the capacitor C1 into the capacitor C2 that had to be carried out in order to reach the voltage threshold across the terminals of C2.
These sensors involve using a switching component we that allows the current to be directed so as to firstly charge up the capacitor C1 and then discharge the capacitor C1 into the capacitor C2 and vice versa. However, this switching component is an element that is difficult to manufacture and whose manufacture is very costly.
A technical problem is therefore posed for the construction of a current-reversing circuit such that the circuit can go from a circuit for charging a variable capacitive structure, whose capacitance variation it is desired to detect, to a circuit for discharging this capacitive structure.
In the following, ‘variable capacitive structure’ is understood to mean any hardware configuration formed by a capacitive electrode integrated into an object or into a system and via its near environment connected directly or indirectly to a ground reference, this environment being able to include a part of the body of a user whose presence must be detected.